Current interrupting device



2 Sheets-Sheet l P. B. HOYE CURRENT INTERRUPTING DEVICE Sw .QN

Filed Oct. 6, 1950 ,sept 13, 1955 IN1/EN TOR. @d6/E Qg/ /L'Luu ,ma @SM Sept. 13, 1955 P. B. HOYE 2,717,939

CURRENT INTERRUPTING DEVICE Filed Oct. 6, 1950 2 Sheets-Sheet 2 INVENTOR.

United States Patent O CURRENT NTERRUPTNG DEVICE Peder Br Hoye, Maywood, lil., assignor to Electrical Engineers Equipment Co., Melrose Park, lili., a corporation of Illinois Application October 6, 1950, Serial No. 188,714

15 Claims. (Cl. 28d-149) This invention pertains generally to a current interrupting device and, more particularly, to such a device as will positively break an electrical circuit and discontinue further flow therethrough.

While the improvements of this invention are adapted for a wide variety of current interrupting devices of the i.

type indicated above, it will be illustrated in connection with a current interrupting device generally referred to as an air circuit interrupter. Such description is, however, by way of illustration and not by way of limitation.

lt is one of the objects of this invention to provide an operating mechanism for actuating one of the two relatively movable arcing contacts, which mechanism is relatively inexpensive to produce and which consists of simple operating elements.

lt is another object of the invention to provide operating mechanism which includes as a positive element of the linkage, resilient means, preferably in the form of a metal spring. The spring is so formed and interrelated with the other structure as to occupy a small space.

It is a further object of the invention to employ the spring element mentioned above as the means for quickly moving the relatively movable contact to open or closed position, said spring, however, not being loaded in either the open or closed position. Consequently, the life of the spring will be greater and less subject to variations in its resiliency and also there is no need for any latching means. In this connection, however, some slight prestressing of the spring may be employed in order to pre vent the relatively movable contact from being vibrated toward the opposite position or from being moved by other end loading. This pre-stressing is, however, nothing like the stressing resulting when the spring means is loaded to actuate the movable contact.

It is yet another object of the invention to provide operating mechanism which may be compactly arranged and interconnected and in which a number of the operating elements may be mounted about a single axis.

lt is yet a further object of the invention to provide in the current interrupting device one of the two relatively movable contacts with a plurality of spring lingers disposed about a center for receiving the other contact, with extensions on some but not all of said Contact fingers and with the extensions being formed of metal which is more resistive to destruction by arcing than the metal of the fingers themselves. Such extensions are then adapted to draw the are without it being necessary to dispose such metal on all of the arcing ends of the fingers. This results in fewer parts and less labor. The extensions need not, but may, have a common contact engaging surface with their respective fingers but preferably are disposed in some regular pattern such, for example, as a pair diametrically opposed to each other in a contact having four contact fingers. lt will be appreciated, however, that such extensions may be employed singly or in an irregular pattern at the arcing ends of the fingers within the scope of this invention.

It is yet another object of the invention to provide in 2,717,939 Patented Sept. 13, 1955 the current interrupting device of my invention improved means for extinguishing the arc drawn between the relatively movable contacts, such means comprising one or more liner rings surrounding the movable contact with the liner rings being disposed within an insulating tube and providing a circumferential groove on the exterior surface of the ring and a tapered throat on the inner surface of the ring. By means of such tapered inner surface the gases resulting from arcing may be directed inwardly toward the arc in a concerted manner to more quickly extinguish it and the groove on the exterior surface will serve to resist gas flow along the exterior surface of the ring between it and the insulating tube and, in some forms of the groove, may assist in directing in the desired direction any gaseous discharge which does tend to flow between the ring and the tubular member.

Further objects, uses and advantages of the invention will become apparent, or be obvious, from a consideration f the following description, when taken with the drawings, in which:

Figure l is a vertical, sectional view of my invention embodied in an air circuit interrupter;

Figure 2 is a sectional view on the line 2-2 of Figure l;

Figure 3 is a fragmentary sectional View, similar to that of Figure l, showing the operating mechanism in a position just before the movable Contact is moved from circuitclosed position to circuit-open position;

Figure 4 is a fragmentary sectional view, similar to that of Figure l, showing the operating mechanism with the movable Contact in open-circuit position;

Figure 5 is a fragmentary sectional view of an improved arcing contact of slightly modied form from that illustrated in Figure l;

Figure 6 illustrates a modified form of liner ring from that shown in Figures l and 5;

Figure 7 shows yet another modification of the liner ring illustrated in Figures l and 5;

Figure 8 is an end view of the fixed contact of Figure 5;

Figure 9 is a side elevation of a modified form of arcing contact, partially in section; and

Figure l0 is an end view of the arcing contact o Figure 9.

Referring now more particularly to Figures 1 through 4, the current interrupting device is indicated generally by the reference numeral 10 and, broadly speaking, consists of a housing 12 for the operating mechanism and what might be called a tubular insulating structure 14 for the relatively movable contacts. The housing 12 and tubular structure 14 are connected together and the tubular insulating structure 14 may take any one of a number of forms. The form shown comprises an outer porcelain sleeve 16 within which there is disposed radially inwardly, in sequence, a sleeve 18 of electrical insulating material such as liber, a second fiber tube 20 and a plurality of liner rings 22 which will be described more particularly hereinafter. Sleeve 16 is cemented as at 24 to the end members 26 and 28 at their respective flanges and 32. Sleeves 18 and Ztl may bear against a Washer 34 which, in turn, abuts against a shoulder 36 of the end member 28 and, at their other ends, the sleeves 18 and 20 face the radially extending flange 38 of the rear stationary contact which is indicated generally by the reference numeral 40. Contact 40 has axially extending spring fingers 42 which are urged radially inwardly into Contact with the movable contact 44 by a garter spring 46. End member 26 is electrically conductive and abuts against the rear stationary Contact 40 at the flange 38 of the latter and said end member 26 has a mounting flange 48 which is adapted to fit against and be secured to the mounting flange S0 of the housing 12, said housing 12 also being electrically conductive. An insulating Washer 52 and the liner rings 22 are disposed about the movable contact 44 and extend between the rear stationary contact and the front stationary, or relatively fixed, contact 54.

Contact 54 has a plurality of spring lingers 56 which are spaced about a center and are adapted to engage the movable contact 44 between their ends. The fingers S6 are joined at a base portion 53 which has secured to it a contact cap (also serving as a gas condenser) which, for example, is adapted to be engageable with a U-shaped spring contact (not shown). Movable contact 44 preferably has at its end 62 a material which is more resistive to destruction from arcing than the main body of the movable contact. Secured to the movable contact 44, axially beyond the end 62, is a follower tube 64 of insulating material which, when drawn axially into the arcing chamber, that is, into the space surrounded by rings 22, tends to till the arcing chamber and helps to assist in the destruction of any arc which is formed.

lt will be readily seen that when the current interrupting device is in the position shown in Figure l, that is, in the closed-circuit position, the electrical circuit through the device-for example, from the right-hand end of Figure l-will be from the cap 60 to the base portion 5S of the relatively fixed, or front stationary, contact 54 to the end of the relatively movable contact 44 and through it to the rear stationary contact 40, thence to the end member 26 and to the housing 12. The whole current interrupting device 1t) may be mounted for rotation, for example, on the shaft 64 (see Figure 2) which extends outwardly of the housing 12. A pigtail, or other exible conductor (not shown) may be secured to an appropriate portion of the housing 12 in order to continue the circuit to a contact mounted in some stationary fashion. so mounted, it is possible for it to form a switch element which is rotatable out of engagement by its cap 60 (or by some other appropriate conductive element which is electrically connected with the relatively fixed contact 54) with another contact (not shown) in order to provide an air break in the circuit, in addition to the separation provided through separation of the relatively movable contacts 44 and 54.

Shaft 64 is pivotally mounted in the housing 12 and is connected, interiorly of housing 12, with a driver 66 which may be stamped from sheet metal and formed as an inverted, generally U-shaped member, as best shown in Figure 2. Driver` 66 carries a roller 68 at its lower end between its arms 72 and 72 and on a pin 70. The arm 72 of the driver 66 carries a pair of spaced apart blocking elements, or cams, 74 and 74 for a purpose to be described below. Roller 68 cooperates with a cam member, indicated generally by the reference numeral 76, which cam member has arms 78 and 78 which are adapted to be movable through the arms 72 and 72 of the driver 66.

T he arms 78 and 78 have on their inner sides arcuate surfaces 75 and 75', respectively, the radii of said arcs corresponding to the distance from the axis of rotation of the driver to the outermost edge of the roller 68. Consequently, the arcuate surfaces provide idling surfaces opposing the roller but not moved by pressure of the roller thereon. Over-travel is permitted to roller 68 by arcuate surfaces 75 and 75 without affecting the fixed trip open and trip close positions. Consequently, the current interrupting device 10 may itself be rotated as a switch blade to a closed circuit position (not shown), for example, before the movable contact in device lil has been closed.

Arcuate surfaces and 75 each join motion-imparting surfaces 77 and 77 on the cam member 76, each of which surfaces when pressed on by the roller 68 of driver 66 will cause the cam member 76 to rotate about its axis on pivot pin St?. Motion-imparting surfaces 77 and 77' form the side walls of a slot 79 of the cam member 76.

With the current interrupting device As may be best seen from Figure 2, the cam member 76 is pivotally mounted on pivot pin 80 which is supported in the walls of the housing 12 and said cam member is connected by a pair of straps 82 and 82' to a pair of spaced apart, generally triangular plates 84 and which carry a spring loading pin 86 between them. The plates 84 and 84 are also pivotally mounted on pivot pin 80. The straps 82 and 82 and plates 84 and 84 serve generally to encase the spring means which is indicated generally by the reference numeral 88. The spring means preferably comprises a coiled spring having arms and 90', said coil spring encircling the pivot pin 89 and being supported in part on an inner circular block 92 which may be supported on pivot pin 80, or from plates 84 and S4', and which, together with the straps 82 and 32 and plates S4 and 84', forms the spring supporting means.

Also pivoted on pivot pin Si) are a pair of spaced apart elements 94 and 94 which carry a pin 96, which may be referred to as a spring restraining pin, and which also carry a restraining pin 98 where the spaced apart elements "4 and 9&3 come into closer parallelism. Pin 98 is adapted o cooperate with the blocking elements 74 and 74 of the river 66 for a purpose to be explained below. At their vuter ends the spaced apart elements 94 and 94 carry between them a roller HM) which is adapted to cooperate with n contact carrying member, or cradle, indicated generally by the reference numeral 102. The spaced apart elements 94 and 94 constitute a contact actuating arm and, hereinafter, will frequently be referred to by that name and identified by numeral 95.

The connection between the contact actuating arm 9S and the cradle 102 is a lost motion connection, since a passageway 194 is provided between walls of the cradle within which passageway the roller 10) is adapted to move backwardly and forwardly depending upon the direction of movement and location of the actuating arm 95. Fianges 106 formed on the cradle, or contact carrying member, 162 provide a pair of oppositely disposed guideways (Figure 2). A pair of rods 110, 110 supported in the housing 12 provide guide members which fit within the guideways 198 in order to guide the movable contact positively in a straight line motion when it is moved.

Referring now to Figure 5, the improved liner rings 22 rf my current interrupting device will oe shown on larger scale and be described more in detail. It will be seen that each ring 22 has on its inner surface a short leading portion 112 which closely parallels and is concentric with the movable contact 44, said contact being shown in a position of withdrawal from a relatively xed contact 54a which will be described hereinafter. The remainder of the inner surface of each ring 22 is tapered as at 114 and the outer surface 116 has a short leading portion of reduced diameter, and bevelled, as indicated at 118, the bevel being of the same angular extent as that of the inner tapered surface 114. The reduced diameter 118 permits the ring to nest within the tapered portion of a ring which may lie ahead of it. In the outer cylindrical surface 116 which has a relatively close fit within the tubular sleeve 26, there is disposed a groove 129 of generally triangular cross section.

Groove 12() is formed by a wall 124 which lies in a plane substantially perpendicular to the axis of the ring and by an intersecting wall 126 which is inclined at an angle to wall 124. Gases which may be generated by the arc formed during the separation of the contacts and which may seek to pass in the direction of the movable Contact will be slowed up and resisted by the presence of the grooves 12d so that the ilow of gases toward thc operating mechanism in housing 12 will be minimized. Furthermore, the shape of grooves 120 in rings 22 is such that some of the gas will be directed radially outwardly and toward the fixed Contact 54 of Figure l, or 54a of Fignlre 5, along the small annular passageway 12S between the outer surface 116 of the rings 22 and the inner surface of the fiber sleeve 20. This directional flow is caused by the shape and direction of the walls 124 and 126 of the groove 120.

On the inner surface of the rings 22 the tapered surface 114, together with the end surface 130 of the immediately following ring 22, will tend to direct the gases, resulting from arcing, into the path of the arc, to thereby assist in extinguishing said arc. Rings 22 are preferably composed of an insulating material which has a high ability to withstand the destructive action of the electric arc, but which at the same time permits a certain amount of burning so that a substantial amount of gas is produced to quench the arc. Such a material is typically represented by horn libre or the like.

ln Figure 6 a modification of a liner ring is indicated generally' by the reference numeral 22a. Ring 22a is similar to ring 22 shown in Figures 1 and 5, with the exception that the groove 120m in the outer surface 116a of the ring is arcuate in cross section.

ln Figure 7 there is illustrated yet another modification of the liner ring 22 of Figures l and 5, said ring being indicated generally by the reference numeral 22b. The ring is similar in all respects to that of Figures 1 and 5, except that the groove 120b in its outer surface 116!) is rectangular in cross section.

Referring now more particularly to Figures 5 and 8, a form of contact 54a will be described. Contact 54a is a female contact similar to that shown in Figure 1, with the exception that the contact fingers 56a are shorter than those of Figure 1, there is a reduced diameter of the fingers adjacent base portion 58a, and said base portion is of a greater outside diameter than that of the combined fingers 56a. However, insofar as the improvement which will now be described is concerned, the contacts of Figures l and 5 are the same', since at least one, but not all, of the fingers 56a have on their arcing ends 134 extensions 132 formed of a material which is more resistive to destruction by arcing than the material of which the lingers themselves are formed. The extensions may be formed, for example, of a silver tungsten alloy, while the fingers themselves may be formed of copper or copper alloy. While contacts 54 and 54a of Figures 1 and 5, respectively, are shown as fixed contacts, for the purposes of the improvement now being described they could be movable, or relatively movable, contacts just as well.

It will be observed that the extensions 132 protrude an equal amount axially beyond the arcing ends 134 of the lingers 56a and are, therefore, closer to the movable contact 44 after it is withdrawn from the contact 54a, so that any arcing will be drawn between the arcing tip 62 of the movable contact 44 and the extensions 132. lt has been found that these extensions will safely take the heat generated by the arc without the necessity of completely covering the arcing ends 134 of the iingers @6a with such material, thereby reducing the amount of silver tungsten which is used and also reducing the amount of labor involved in assembling the silver tungsten on the fingers, since only certain ones of them need to carry such extensions. Preferably, the extensions protrude in the direction of separation of the contacts the same amount and preferably they are disposed in a regular pattern with respect to each other, although it is not necessary that they be so disposed to come within the scope of this invention. In Figures 5 and 8 it will be seen that the ex tensions 132 are of lesser arcuate dimension than the arcing ends of their respective fingers 56a and that they are disposed diametrically opposite from each other, that is to say, in a regular pattern when considered with respect to the circumference of the group of fingers 56a. As shown, the extensions are so disposed that they form a continuing axially extending surface 136, when considered with respect to the axially extending gripping surface 138 of the fingers so that as the movable contact leaves the fixed contact the arc which is generated will tend to be taken on the outer surfaces of the extensions 132 instead of on the surfaces 136, as might be the case if the extensions 132 were set radially outwardly with respect to the surfaces 138 of the fingers 56a. However, the extensions 132 may have their surfaces 136 set back radially from the position shown, that is, not be flush with surfaces 138 of the fingers, and still operate in an entirely satisfactory manner.

In Figures 9 and 10 a modification of the female arcing contact of Figure 5 is illustrated. This arcing contact is indicated generally by the reference numeral 54h and will be considered the same as that of 54a with the exceptions now to be noted. The extensions 132 of the contact 54h are formed of a metal more resistive to destruction from arcing than the metal of the fingers, which extensions comprise a pair of flat portions 133 on either side of a portion 135 which protrudes farther in the direction of separation of the contacts than do the flat portions 133. The portions 133 and 135 are formed, for example, of a tungsten silver alloy. The protruding portion 135 may be a separate piece or may be formed integrally with the fiat portions 133. 1t will be noted that the extensions 132 here extend arcuately the same amount as the arcing ends 134 of the fingers themselves and have an aligned, or continuing, axially extending inner surface 136', aligned with the inner gripping surface 138 of the finger. With such construction, a flat arcuate silver tungsten extension 137 may be placed, if desired, on the arcing ends of each of the other fingers which do not carry the protruding portion 135. This will provide greater protection for the ends of the fingers 56b, but is not essential.

The base portion 58b of the arcing Contact 54b has a greater outside diameter than the outside diameter of the combined fingers 56h. This permits the employment of resilient means such as individual spring fingers 140, each of which is carried by the base portion 581; in a recess 141, into which one end of the spring is fitted. The free end of each spring 140 then bears against the outer surface of a linger 5611 adjacent its arcing end, thereby tending to further the spring action of the finger 56h and urge it radially inwardly to grip the movable contact 44. If necessary, the connection of the springs 140 with the base portion 58h may be supplemented by welding, etc., although a friction fit is possible in the recesses 141. It will be observed that the arched portion 142 of each of the springs preferably is of such shape that the spring lies radially inwardly of the outside diameter of the base portion 58h.

Because a smaller diameter is provided, as at 144, in the fingers 56b, a shoulder 146 is provided and it would be readily possible to secure the ends of spring member 140 to such a flat shoulder, or to other surface within the reduced diameter 144, instead of inserting them in recesses 141 in the base portion 58b.

Turning now to the entire mechanism as illustrated in Figures l through 4, the operation of the device will now be described. As shown in Figure 1, the interrupter unit is in the closed position and the operating mechanism is in the trip close position with the coil spring 88 being slightly pre-stressed, as described above, but not being loaded otherwise. To trip open the device, the shaft 64 is rotated clockwise, in the direction of the arrow of Figure l, and the driver 66 through its roller 68 bears against the motion-imparting cam surface 77 and starts to rotate the cam member 76 in a counterclockwise direction about the pivot pin S0. When the cam member 76 starts rotating, the elements connected with it, including straps 82 and 82 and the plates 84 and 84 and the pin 86 carried by the plates 84 and 84', rotate with it, and the pin 86 acts against the arm 90 of the coil spring 88, urging it in a counterclockwise direction, as viewed in Figures 1 and 3. The other arm 90 of the spring 88 then tends te bear against the pin 96 carried between the elements 94 and 94 of the contact actuating arm 95 so as to cause said arm to rotate in a counterclockwise direction to move the movable contact 44. However, initial rotation of the driver 66 brings its blocking element, or cam, 74 into blocking position with respect to the pin 98 carried by the Contact actuating arm 95, and consequently said arm is restrained against counterclockwise movement and in turn the arm 90 of the coil spring is held against such rotation. Consequently, the movable contact 44 is not yet moved. Further rotation of the driver` 66 continues to hold the contact actuating arm 95 and the spring arm 90 against rotation while the other spring arm 95E is moved by the cam member 76 through the medium of the pin 86 carried by plates 84 and 84. Consequently, the spring is loaded. Arcuate movement of the driver 66 through a 30 angle loads coil spring 83 sufficiently and at that time the blocking element 74 which is carried by the driver 66 moves to an unblocking position whereupon arm 90 of the coil spring 88 very rapidly rotates the contact actuating arm 95 in a counterclockwise direction with it, the restraining pin 98 of said arm then passing over the top of the blocking element 74.

The rapid rotation of the contact actuating arm 9S to the left as viewed in Figures l, 3 and 4 causes said arm, through its roller 1li@ and the lost motion connection of said roller with thc cradle, or contact carrier, 102 and the guide rods llt), to cause the movable contact 44 to he very rapidly separated from the fixed Contact 51.1 in a straight-line motion, thereby breaking the circuit through the current interrupting device il) as soon as the are is extinguished within the arc extinguishing chamber of the tubular portion 14.

Figure 4 illustrates the open circuit position of the device and it will be seen that the spring 88 is now unloaded. If the current interrupting device 10 is so mounted as to form a switch element of a main switch structure (not shown) with which arcing horns (not shown) are employed, the tirst movement of shaft 64 may be employed to cause rotation of interruptor 1t) to open the main switch contacts, followed by loading of spring 8S by driver 66 and then rapid separation of arcing contacts 541 and 44. Then, further clockwise movement of the shaft 6d from the position shown in Figure 4 will cause the arcing horns to separate. During the latter movement, the roller 68 ot the driver 66 will no longer bear against the motion-imparting surface 77 of the cam member 76 but at that point will have reached the arcuate surface 75' along which the roller will idle.

If the contacts 44 and 54- are now to be closed, it will be readily een that rotation of the shaft 64 in a counterclockwise direction as viewed in Figure 4 will initially cause the blocking element 74 of the driver 66 to interfere with the restraining pin 98 carried by the contact actuating arm 95 so that the spring may become loaded, in the same manner as was described during the opening of the circuit. Following a 30 rotation of shaft 64 in the counterclockwise direction, the blocking element will unblock and the loaded spring 8S will very rapidly move contact 444 into engagement with the fixed contact 54.

While I have illustrated preferred embodiments of my invention, l do not intend to be limited thereto, except insofar as the appended claims are so limited, since various suggestions for change and modification will now occur to those skilled in the art by reason of my disclosure.

l claim:

l. An air circuit breaker comprising a relatively fixed arcing contact and a relatively movable arcing Contact, one of said contacts having a plurality of fingers with their ends disposed about a center and adapted to receive the other contact between them, one but not all of said lingers having an extension of metal which is more resistive to destruction from arcing than the metal of said lingers and which protrudes in the direction of separation of the contacts beyond the surface of the other contact fingers, tubular insulating means in which said contacts are disposed, a plurality of liner rings disposed between the relatively movable contact and the insulating tube, said liner rings each having an external circumferential groove and an inner tapered throat, operating means for said relatively movable contact, a housing for said actuating means connected with said insulating tube, a cradle member connected with said relatively movable contact and having a pair of guideways, guide members carried in said housing and cowith said guide.\'ay's, said operating means for the relatively movable contact comprising an actuating arm having a lost motion connection with said cradle and pivoted in said housing, a driver pivotally mounted in the housing and carrying a roller at one end, said driver being operable from the exterior of the housing, a cam member pivotally mounted in the housing and cooperating with said roller, said cam member and contact actuating arm being pivotally supported on the same axis, a coil spring surrounding said axis and operatively interposed between the am member and said contact actuating arm, and blocking means carried by the driver, said blc-cking means blocking movement of the Contact actuating arm during a predetermined moverient of the driver whereby the resilient means is loaded by actuation of said driver, said blocking means unblocking from the contact actuating arm following said predetermined movement whereupon the coil spring acts on the Contact actuating arm to move the relatively movable Contact.

2. In a current interrupting device having a housing and relatively movable contacts for making and breaking a circuit, the combination of a movable contact, a cradle member connected with said contact and having pair of guideways, guide members adapted to be carried in said housing and cooperating with said guideways, operating mechanism for moving said contacts to open-circuit and closed-circuit positions, said mechanism including an actuating arm adapted to be pivotally supported in the housing, and wall means defining a passageway in Said cradle member, said arm carrying a roller member which rides in said passageway and is adapted to bear on said wall means for moving said movable contact.

3. In a current interrupting device having a housing and relatively movable contacts for making and breaking a circuit, the combination of a movable contact, an actuating arm operatively connected therewith and adapted to be pivotally mounted in said housing, a cam member adapted to be pivotally mounted in said housing, resilient means operatively interposed between said cam member and said actuating arm, and a driver adapted to be operated from outside of said housing for imparting movement to said cam member.

4. The combination of claim 3 wherein the driver is adapted to be pivotally mounted in the housing and carries a roller cooperating with said cam member.

5. The combination of claim 4 wherein the cam member has a motion-imparting surface and an idling surface whereby during a portion of the movement of said driver the cam member is actuated therefrom and during another portion of the movement of said driver is not actuated but remains opposed by said roller.

6. The combination of claim 4 wherein the cam member and the contact actuating arm are pivotaily supported on the same axis and wherein the resilient means comprises a coil spring surrounding said axis.

7. The combination of claim 6 wherein the cam member provides a spring supporting structure for the coil spring.

8. For use in an insulating tube of a current interrupting device, a liner rin7 having a cylindrical outer surface with a circumferential groove in said surface spaced from the ends of said surface.

9. The ring of claim 8 wherein the groove is arcuate in cross section.

10. The ring of claim 8 wherein the groove is rectangular in cross section.

11. For use in an insulating tube of a current interrupting device, a liner ring having a cylindrical outer surface with a circumferential groove in said surface, said groove being triangular in cross-section.

12. For use in an insulating tube of a current interrupting device, a liner ring having a cylindrical outer surface with a circumferential groove in said surface, said groove having one wall thereof lying in a plane substantially perpendicular to the aXis of the ring and having another wall inclined at an angle thereto, said ring being formed of an insulating material.

13. In a circuit interrupting device having relatively movable contacts for making and breaking a circuit, the combination of a movable contact, means for rectilinearly moving said movable Contact, an actuating member, resilient means operatively interposed between said contact moving means and said actuating member, blocking means carried by the actuating member and cooperable blocking means carried by said contact moving means, said blocking means and said cooperable blocking means being disassociated when the movable contact is in either its circuit-open position or its circuit-closed position and during its travel between said positions, and cooperating in blocking movement of the contact moving means during an intermediate portion of the movement of the actuating member means, whereby the resilient means is loaded by the actuating member.

14. The combination of claim 3 wherein the movable contact has rectilinear movement.

15. The combination of claim 3 wherein the resilient means comprises a single spring which is prestressed to resist movement of said movable contact from its circuitopen position or circuit-closed position, except when operated by means of said driver.

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